Genetic changes in populations that over time, lead to new organisms. e.g species

Species

A group of organims that can interbreed to produce viable offspring

Deme

A local interbreeding population of speices. Each deme will be fully or partially isolated from other demes.

Cline

A gradual change of species over a geographical gradient. A series of demes along an environmental gradient

Speciation

The process where one or more species is formed from an existing species.

Allopatric Speciation

Formation of a species that are geographically seperated from one another.

Allopatric Speciation Process ( _ Steps)

6 Steps

1. Two populations seperate

2. Gene flow stops

3. Differences in environment mean that natural selection acts differently in the two populations. Individuals best suited to the environemnt will produce more offsping leading to evolutionary changes.

4. Over time, the populations become genetically and phenotypically different.

5. If enough time passes, the populations become so different they are no longer able to interbreed and produce offspring = two new species.

6. If the populations are still able to interbreed with each other, they may be classes as sub-species.

Sympatric Speciation

When species arise without geographical seperation.

Instantaneous Speciation

Where a new species suddenly arises. e.g. Polyploidy

Ecological Speciation

Where one group of individuals in a population adopt a new lifestyle and only breed with individuals who adopt this lifestye.

Polyploidy

Having three or more complete sets of chromosomes.

Non-Disjunction

The failure of chromosomes or chromatids from seperating into different cells during meiosis.

Amphiploidy

The doubling of chromosomes in a hybrid which means chromosomes can now pair up and the hybrid is now fertile. Also known as somatic doubling.

Autopolyploidy

Polyploidy individual resulting from individuals of the same species.

Allopolyploidy

Polyploidy individual resulting from individuals of different species.

What are the major advantages of polyploids?

Bigger, sterile if uneven number of chromosomes. Allopolyploid combines the characteristics of two species.

Reproductive Isolating Mechanisms. (2 Types)

Barriers that prevent species from interbreeding. Prezygotic and Postzygotic